The invention relates to a so-called “fundus camera” for recording an image of the retina in the background of an eye; that is, the “eyeground” or “fundus” of an eye.
Two different procedures are known for the observation of the eyeground.
In the conventional procedure, the eyeground is illuminated using a beam emitted from a light source, and an image is conducted to a sensor by means of an intermediary image using the light reflected or emitted there. This procedure admits of the difficulty that the illumination and the observation must be performed through the iris upon which reflections occur that create image errors.
This procedure was considerably improved by positioning the light source and the detector so that the excitation focus and detector focus were confocal. Thus, optical information coming from other than the focal plane may be easily suppressed, which clearly improves the image quality of the photographs. However, even this result is inadequate to provide some fine details of the eyeground.
Another procedure was therefore developed in which the eyeground is not illuminated completely to its edge, but rather is sampled using a focused light beam and the reflected light is collected by a sensor with a sampling frequency assigned to it. Devices used to obtain this fundus image are called Scanning Laser Opthalmoscopes or Retinal Scanners. A disadvantage of this procedure is that the system required is relatively complex and expensive, and that a time delay arises because of the point-for-point sampling which, in particular, leads to false results because of eye movements. In order to deal with this problem, a wide variety of suggestions have been proposed, each of which causes the system to become more expensive.